The absorption spectra for dimers of Ag(4)(+2) and Ag(8) clusters at various interparticle distances are examined using time-dependent density functional theory (TDDFT) and configuration interaction singles (CIS) calculations. With TDDFT calculations employing the SAOP functional, minor peaks for Ag(4)(+2) and Ag(8) dimers appear as the interparticle distance decreases; these peaks are suggested to be charge transfer artifacts on the basis of CIS and TDDFT (CAM-B3LYP) calculations. The relationship of the absorption peak locations to the distance and orientation between T(d) Ag(20) dimers is also investigated. TDDFT calculations using the SAOP functional are used to determine excitation absorption spectra for eight different orientations of Ag(20) dimers. Although the Ag(20)T(d) monomer has a sharp peak, each dimer absorption spectrum is split due to lower symmetry. This splitting increases as the center of mass distance decreases. As the interparticle distance between the monomers decreases, the initially strong peaks decrease in intensity and red or blue shift depending on symmetry, while the minor peaks increase in intensity and red shift.
"[10–12,14–16]. In one work  the absorption spectra of more complicated complexes, i.e., dimers of silver tetrahedra, Ag þ2 4 and Ag 8 , at various interparticle distances were examined using time-dependent density functional theory (TDDFT) and configuration-interaction singles calculations. This interest on silver clusters is not accidental. "
[Show abstract][Hide abstract] ABSTRACT: Optical absorption spectra of the lowest-energy structures of small and medium-sized transition-metal clusters, Ag-N and Cu-N with N up to 150, are investigated within the classical Mie-Gans theory. The global-minima structures of these clusters have been determined in our previous studies using an unbiased structure-optimization approach combined with the embedded-atom total-energy method. The influence of cluster size, shape and metal on the peak positions and the relative intensities in the absorption spectra is studied systematically. Our studies give information on differences/similarities between optical absorption spectra of different metal clusters and their isomers. The main features of the obtained optical spectra for silver clusters are in good agreement with the available experiments and with results of the computationally much more advanced TDDFF calculations.
[Show abstract][Hide abstract] ABSTRACT: The classification of electronic excitations in molecules and molecular nanostructures plays an important role when tailoring materials with desired properties. One example of such a class of excitations are plasmons. Plasmons appear in solid-state physics, where they are characterized as density oscillations in an electron gas that are driven by the restoring forces associated with the electromagnetic field induced by the density oscillations themselves. Here, we investigate how this concept can be transferred to molecular systems by performing a step-by-step analysis, starting from three-dimensional bulk systems and ending with molecules. On the basis of this analysis, we propose to scale the electron–electron interaction in quantum-chemical response calculations in order to identify plasmons in molecules. This approach is illustrated for molecular chains and clusters. Our results show that the concept of plasmons is still applicable for extended molecular systems and demonstrate that the proposed scaling approach provides an easy way of characterizing electronic excitations.
The Journal of Physical Chemistry C 01/2013; 117(4):1863–1878. DOI:10.1021/jp3113073 · 4.77 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We assess the accuracy of several long-range corrected (LC-) density functionals for the prediction of absorption spectra of silver clusters by time-dependent density functional theory. Several types of LC-functionals, with the exact Hartree-Fock exchange at long range, are used: those applying the long-range correction to a standard GGA-type functional (LC-BP86, LC-ωPBE) or to a local meta-GGA functional (LC-M06L), and two global hybrid functionals (CAM-B3LYP and ωB97x). The spectra calculated with those density functionals are in good agreement with the recent accurate experimental measurements. We show that CAM-B3LYP and ωB97x are ones of the most accurate functionals for evaluating the electronic excitation energies, while LC-M06L is more effective in reducing the occurrence of spurious states. The long-range correction appears to be essential in describing the absorption spectra of large clusters. The description of the plasmon-like band with LC-functionals, as transitions associated to excitations from s orbitals to s + p orbitals, is in fairly good agreement with the classical interpretation as a collective excitation of valence s-electrons.
The Journal of Physical Chemistry A 05/2013; 117(20). DOI:10.1021/jp3124154 · 2.69 Impact Factor
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